Na- Ti- Zr- H2O-rich mineral inclusions indicating postcumulus chrome-spinel dissolution and recrystallization in the Western Laouni mafic intrusion, Algeria

摘要: Disseminated cumulus chrome spinel in the lower-most olivine orthocumulates from Western Laouni intrusion (Southern Hoggar, Algeria) contains inclusions of silicates enriched Mg-Ti-Na and H2O, Fe-Ti (Zr) rich oxides, occurring either as numerous micro-inclusions or large solitary cavities. Regardless inclusion type, titanian pargasite (or kaersutite) sodium analog phlogopite predominate over orthopyroxene (En86 to En92) Na-rich plagioclase (An50Ab50 An7Ab93). Oxide are magnesian ilmenite (up 37 mol% MgTiO3), rutile, loveringite (Ca,REE-(Ti,Fe,Cr,Mg,Zr)21O38) accessory pseudo-brookite (“kennedyite”); apatite, Fe-Ni-Cu sulfides alteration products (saussurite, bastite) also present. Apart kennedyite, all minerals included form larger intercumulus crystals host rock well. The were trapped consequence dissolving against liquid, 150 300° C below its liquidus temperature. cavities attributed fluid-assisted solid-state recrystallization chains crystals; role capillary fluids is demonstrated by both hydrous nature solid a strong positive correlation between amphibole content abundance rock. Phlogopite locally showing similar optical orientation within outside indicates that was still recrystallizing down 950° C. In temperature range 1100-900° determined for formation inclusions, probably various combinations crystals, liquids fluids, respective quantities which varied greatly distances few tens micrometres single spinel. volume ratio solids must have been low enough permit magmatic hydrothermal reactions, otherwise never possible crystals. Hence, lack clinopyroxene while abundant suggests that, trapped, they completely reacted with residual liquid respectively. Likewise, Na albite Na-phlogopite mineral inclusions.